Chemical mechanical polishing slurry useful for copper substrates

ABSTRACT

A chemical mechanical polishing slurry comprising a film forming agent, an oxidizer, a complexing agent and an abrasive, and a method for using the chemical mechanical polishing slurry to remove copper alloy, titanium, and titanium nitride containing layers from a substrate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention concerns a chemical mechanical polishing slurry includinga complexing agent, at least one oxidizer, at least one abrasive, and afilm forming agent. The chemical mechanical polishing slurry is usefulfor polishing metal layers and thin-films associated with semiconductormanufacturing. More particularly this invention concerns a chemicalmechanical polishing slurry that is especially adapted for polishingmultiple metal layers and thin-films where one of the layers or films iscomprised of copper or a copper containing alloy.

2. Description of the Art

Integrated circuits are made up of millions of active devices formed inor on a silicon substrate. The active devices, which are initiallyisolated from one another, are interconnected to form functionalcircuits and components. The devices are interconnected through the useof well-known multilevel interconnections. Interconnection structuresnormally have a first layer of metallization, an interconnection layer,a second level of metallization, and sometimes a third and subsequentlevel of metallization. Interlevel dielectrics such as doped and undopedsilicon dioxide (SiO₂), are used to electrically isolate the differentlevels of metallization in a silicon substrate or well. The electricalconnections between different interconnection levels are made throughthe use of metallized vias. U.S. Pat. No. 4,789,648, which isincorporated herein by reference, describes a method for preparingmultiple metallized layers and metallized vias in insulator films. In asimilar manner, metal contacts are used to form electrical connectionsbetween interconnection levels and devices formed in a well. The metalvias and contacts may be filled with various metals and alloys includingtitanium (Ti), titanium nitride (TiN), tantalum (Ta), aluminum copper(Al--Cu), aluminum silicon (Al--Si), copper (Cu), tungsten (W), andcombinations thereof. The metal vias and contacts generally employ anadhesion layer such as titanium nitride (TiN) and/or titanium (Ti) toadhere the metal layer to the SiO₂ substrate. At the contact level, theadhesion layer acts as a diffusion barrier to prevent the filled metaland SiO₂ from reacting.

In one semiconductor manufacturing process, metallized vias or contactsare formed by a blanket metal deposition followed by a chemicalmechanical polish (CMP) step. In a typical process, via holes are etchedthrough an interlevel dielectric (ILD) to interconnection lines or to asemiconductor substrate. Next, a thin adhesion layer such as titaniumnitride and/or titanium is generally formed over the ILD and is directedinto the etched via hole. Then, a metal film is blanket deposited overthe adhesion layer and into the via hole. Deposition is continued untilthe via hole is filled with the blanket deposited metal. Finally, theexcess metal is removed by chemical mechanical polishing, (CMP) to formmetal vias. Processes for manufacturing and/or CMP of vias are disclosedin U.S. Pat. Nos. 4,671,851, 4,910,155 and 4,944,836.

In a typical chemical mechanical polishing process, the substrate isplaced in direct contact with a rotating polishing pad. A carrierapplies pressure against the backside of the substrate. During thepolishing process, the pad and table are rotated while a downward forceis maintained against the substrate back. An abrasive and chemicallyreactive solution, commonly referred to as a "slurry" is applied to thepad during polishing. The slurry initiates the polishing process bychemically reacting with the film being polished. The polishing processis facilitated by the rotational movement of the pad relative to thesubstrate as slurry is provided to the wafer/pad interface. Polishing iscontinued in this manner until the desired film on the insulator isremoved. The slurry composition is an important factor in the CMP step.Depending on the choice of the oxidizing agent, the abrasive, and otheruseful additives, the polishing slurry can be tailored to provideeffective polishing to metal layers at desired polishing rates whileminimizing surface imperfections, defects and corrosion and erosion.Furthermore, the polishing slurry may be used to provide controlledpolishing selectivities to other thin-film materials used in currentintegrated circuit technology such as titanium, titanium nitride and thelike.

Typically CMP polishing slurries contain an abrasive material, such assilica or alumina, suspended in an oxidizing, aqueous medium. Forexample, U.S. Pat. No. 5,244,523 to Yu et al. reports a slurrycontaining alumina, hydrogen peroxide, and either potassium or ammoniumhydroxide that is useful to remove tungsten at predictable rates withlittle removal of the underlying insulating layer. U.S. Pat. No.5,209,816 to Yu et al. discloses a slurry comprising perchloric acid,hydrogen peroxide and a solid abrasive material in an aqueous mediumthat is useful for polishing aluminum. U.S. Pat. No. 5,340,370 to Cadienand Feller discloses a tungsten polishing slurry comprisingapproximately 0.1M potassium ferricyanide, approximately 5 weightpercent silica and potassium acetate. Acetic acid is added to buffer thepH at approximately 3.5.

U.S. Pat. No. 4,789,648 to Beyer et al. discloses a slurry formulationusing alumina abrasives in conjunction with sulfuric, nitric, and aceticacids and deionized water. U.S. Pat. Nos. 5,391,258 and 5,476,606disclose slurries for polishing a composite of metal and silica whichincludes an aqueous medium, abrasive particles and an anion whichcontrols the rate of silica removal. Other polishing slurries for use inCMP applications are described in U.S. Pat. No. 5,527,423 to Neville etal., U.S. Pat. No. 5,354,490 to Yu et al., U.S. Pat. No. 5,340,370 toCadien et al., U.S. Pat. No. 5,209,816 to Yu et al., U.S. Pat. No.5,157,876 to Medellin, U.S. Pat. No. 5,137,544 to Medellin, and U.S.Pat. No. 4,956,313 to Cote et al.

There are various mechanisms disclosed in the prior art by which metalsurfaces can be polished with slurries. The metal surface may bepolished using a slurry in which a surface film is not formed in whichcase the process proceeds by mechanical removal of metal particles andtheir dissolution in the slurry. In such a mechanism, the chemicaldissolution rate should be slow in order to avoid wet etching. A morepreferred mechanism is, however, one where a thin abradable layer iscontinuously formed by reaction between the metal surface and one ormore components in the slurry such as a complexing agent and/or a filmforming layer. The thin abradable layer is then removed in a controlledmanner by mechanical action. Once the mechanical polishing process hasstopped a thin passive film remains on the surface and controls the wetetching process. Controlling the chemical mechanical polishing processis much easier when a CMP slurry polishes using this mechanism.

Efforts to develop copper CMP slurries are disclosed in the literature.The RPI effort (J. M. Steigerwald et al, Electrochemical PotentialMeasurements during the Chemical-Mechanical Polishing of Copper ThinFilms, Mat. Res. Soc. Symp. 337, 133 (1994)) is focused on the use ofammonium compounds (ammonium nitrate, chloride, hydroxide), nitric acid,and alumina abrasive. Copper dissolution of 2 nm/min (as measuredelectrochemically) is assumed to proceed from a film-free surface.Polishing rates, however, are reported to be in excess of 400 nm/min.The discrepancy is explained by importance given to the mechanicalaction, forming Cu debris, which is then dissolved by solution.Selectivity factors are not given.

Q. Luo et al, Chemical-Mechanical Polishing of Copper in Acidic Media,Proceedings--First International Chemical-Mechanical Polish (CMP) forVLSI/LSI Multilevel Interconnection Conference (CMP-MIC), Santa Barbara,Feb. 22-23, (1996) discloses using a CMP slurry including a veryaggressive etchant, Fe-nitrate, pH 1-2, in combination with an inhibitor(benzotriazole), a slurry stabilizing surfactant (poly-ethylene-glycol)and alumina. The chemical reaction is apparently controlled by aformation of a corrosion inhibiting film, namely Cu-BTA, with surfactantundermining its protectiveness. Selectivity to oxide is given as 15:1 to45:1.

CMP electrochemical work at Sematech laboratories is disclosed in R.Carpio et al, Initial Study On Copper CMP Slurry Chemistries, Thin SolidFilms, 262 (1995). The reference explores the use of electrochemistry inthe fundamental characterization of plausible slurries. In addition toseveral others, potassium permanganate is used as a slurry oxidizer.

H. Hirabayashi et al, Chemical Mechanical Polishing of Copper Using ASlurry Composed of Glycine and Hydrogen Peroxide, Proceedings--FirstInternational Chemical-Mechanical Polish (CMP) for VLSI/LSI MultilevelInterconnection Conference (CMP-MIC), Santa Barbara, Feb. 22-23, (1996),and Japanese Kokai Patent Application No. 8 (1996) 83780 disclose amixture of glycine, hydrogen peroxide and silica, with or withoutbenzotriazole, for the CMP process of Cu with a low corrosion rate anddefect level. The references disclose that CMP slurries incorporating achemical agent, such as benzotriazole andn-benzoyl-n-phenylhydroxylamine form a protective film on copper. Theremoval rate varies, depending on the concentration of slurrycomponents. An optimized rate of 120 nm/min was reported, with TiN rateof 30 nm/min and dishing of 200 nm across the 15 μm wide structures.

Several relevant Cu chemistries have been discussed in the openliterature, each failing to deliver a process which successfullyaddresses all of the key requirements of a chemical-mechanical polishingslurry; namely metal removal rate of more than 200 nm/min, rateselectivity to metal liners of <5, selectivity to dielectric oxide layerof >50 and overall defect depth of <10%.

Despite the desirability of using a film forming mechanism in a CMPprocess there remains problems with formulating CMP slurries that cancontrol the thickness of the layer of film formed as well as problemsensuring that the film formed is abradable. These problems can result ina CMP slurry that exhibits unacceptably low polishing rates or poorpolishing results. Thus, a need remains for a CMP slurry that is capableof forming a removable thin abradable layer on a substrate surface andmore particularly on the surface of a copper alloy containing substrate.A desireable CMP slurry will exhibit good thin film polishingselectivities and simultaneously give polished substrates with minimaldishing and low defectivity.

SUMMARY OF THE INVENTION

The present invention is directed to a chemical mechanical polishingslurry that is able to polish metal containing substrates at acceptablerates.

In addition, the chemical mechanical polishing slurry has a lowinsulator polishing selectivity while exhibiting high polishingselectivities towards copper and copper alloy containing metal layers.

Furthermore, this invention is directed to methods for using a singlechemical mechanical polishing slurry to polish metal layers andparticularly copper or copper alloy containing layers in an integratedcircuit.

In one embodiment, this invention is a chemical mechanical polishingslurry. The CMP slurry includes an abrasive, an oxidizer, a complexingagent, and a film forming agent. In a preferred embodiment the CMPslurry includes from about 1.0 to about 15.0 weight percent of analumina abrasive, from about 0.3 to about 12.0 weight percent hydrogenperoxide, from about 1.0 to about 3.0 weight percent ammonium oxalate,and from about 0.01 to about 0.2 weight percent benzotriazole. Inanother preferred embodiment the CMP slurry includes 1.0 to about 15.0wt % alumina abrasive, from about 1.0 to 10.0 wt % urea peroxide, from1.0 to 3.0 wt % ammonium oxalate and from about 0.01 to about 0.2 wt %benzotriazole. All CMP slurry embodiments include deionized water aswell.

In another embodiment, this invention is a method for polishing asubstrate including at least one metal layer. The method begins bymixing from about 1.0 to about 15.0 weight percent of an abrasive, fromabout 0.3 to about 12.0 weight percent of an oxidizer, from about 0.5 toabout 3.0 weight percent of at least one complexing agent, from about0.01 to about 0.2 weight percent of at least one film forming agent, anddeionized water to give a chemical mechanical polishing slurry. Next,the chemical mechanical polishing slurry is applied to the substrate.Finally, at least a portion of the metal layer is removed from thesubstrate by bringing a pad into contact with the substrate and movingthe pad in relation to the substrate.

FIG. 1 shows potentiodynamic polarization curves measured on copper insolutions containing 4 weight % of ammonium persulfate and either 1weight % glycine (curves 1 & 2) or 1 weight % ammonium oxalate (curves 3& 4). Each set of curves was measured during copper surface abrasion(curves 1 & 3), and again after abrasion had ceased (curves 2 & 4).

FIG. 2 shows potentiodynamic polarization curves on copper in: 11% H₂ O₂wt % oxidizer solution (curve 1 after abrasion); in electrolyte with thesame oxidizer and 1 wt % glycine (curve 2, after abrasion); and in thesame oxidizer with 1 wt % ammonium oxalate (curve 3, also afterabrasion).

FIG. 3 shows the reproducibility of the polishing performance, i.e.,polishing rate and within wafer non-uniformity, for copper using a CMPslurry of this invention comprising 5.0 wt % alumina abrasive, 11.0 wt %H₂ O₂, 1.5 wt % ammonium oxalate, 0.04 wt % benzotriazole, and 50 ppmwetting agent (TRITON® DF-16).

DESCRIPTION OF THE CURRENT EMBODIMENT

The present invention relates to a chemical mechanical polishing slurrythat comprises an abrasive, at least one oxidizer, a complexing agentand a film forming agent. The chemical mechanical polishing slurry isespecially useful for polishing copper and copper alloy containing metallayers associated with a substrate selected from the group includingintegrated circuits, thin films, multiple level semiconductors, andwafers.

Before describing the details of the various preferred embodiments ofthis invention, some of the terms that are used herein will be defined.The chemical mechanical polishing slurry, ("CMP slurry"), is a usefulproduct of this invention that comprises an oxidizer, an abrasive, acomplexing agent, a film forming agent, and other optional ingredients.The CMP slurry is useful for polishing a multiple level metallizationwhich may include but are not limited to semi-conductor thin-films,integrated circuit thin-films, and for any other films and surfaceswhere CMP processes are useful. The terms "copper" and "coppercontaining alloys" are used interchangeably herein as it is within theunderstanding of one of skill in the art that the terms include but arenot limited to substrates comprising layers of pure copper, copperaluminum alloys, and Ti/TiN/Cu, and Ta/TaN/Cu multi-layer substrates.

The CMP slurry of this invention includes at least one oxidizer. Theoxidizer aids in oxidizing the substrate metal layer or layers to theircorresponding oxide, hydroxide, or ions. For example, in the presentinvention, the oxidizer may be used to oxidize a metal layer to itscorresponding oxide or hydroxide, e.g., titanium to titanium oxide,tungsten to tungsten oxide, copper to copper oxide, and aluminum toaluminum oxide. The oxidizing agent is useful when incorporated into aCMP slurry to polish metals and metal based components includingtitanium, titanium nitride, tantalum, copper, tungsten, aluminum, andaluminum alloys such as aluminum/copper alloys, and various mixtures andcombinations thereof by mechanically polishing the metals to remove therespective oxide layer.

The oxidizer used in the CMP slurry of this invention may be selectedfrom compounds which, upon reduction, form hydroxyl radicals. Suchoxidizers exhibit good polishing selectivity towards metal and metalcontaining substrate layers and particularly towards copper alloylayers. Non-exclusive examples of metal oxidizing compounds that, uponreduction, form hydroxyl radicals include peracetic acid, urea-hydrogenperoxide and hydrogen peroxide and mixtures thereof, with hydrogenperoxide being a preferred oxidizer. The oxidizer may be present in thechemical mechanical polishing slurry in an amount ranging from about 0.3to about 20.0 weight percent. It is preferred that the oxidizer ispresent in the CMP slurry of this invention in an amount ranging fromabout 0.3 to about 15.0 weight percent and most preferably from about1.0 to about 12.0 weight percent.

The CMP slurry of this invention also includes a film forming agent. Thefilm forming agent may be any compound or mixtures of compounds that arecapable of facilitating the formation of a passivation layer of metaloxides and dissolution inhibiting layers on the surface of the metallayer. Passivation of the substrate surface layer is important toprevent wet etching of the substrate surface. Useful film forming agentsare cyclic compounds such as imidazole, benzotriazole, benzimidazole andbenzothiazole and their derivatives with hydroxy, amino, imino, carboxy,mercapto, nitro and alkyl substituted groups, as well as urea, thioureaand others. A preferred film forming agent is benzotriazole ("BTA"). Thefilm forming agent should be present in the chemical mechanicalpolishing slurry of this invention in an amount that is capable ofpromoting quick, and preferably almost instantaneous formation ofpassivating layers and dissolution inhibiting layers on the substratesurface. The film forming agent should be present in the CMP slurry ofthis invention in an amount ranging from about 0.01 weight percent toabout 1.0 weight percent. It is preferred that film forming agent ispresent in the CMP slurry in an amount ranging from about 0.01 to about0.2 weight percent.

Once a passivation layer has formed on the substrate surface it becomesimportant to be able to disturb the passivation layer in order to abrademetal oxides from the substrate surface with the abrasive component ofthe CMP slurry of this invention. One class of compounds that is usefulin disturbing the passivation layer are complexing agents. Usefulcomplexing agents include but are not limited to acids such as citric,lactic, tartaric, succinic, acetic, oxalic and other acids, as well asamino acid and amino sulfuric acids and their salts. A preferredcomplexing agent is ammonium oxalate.

The complexing agents serve at least two useful functions in the CMPslurry of this invention. The complexing agent disturbs the passivationlayer during the mechanical abrasion step without destroying the layeror inhibiting its formation during the abrasion step and especiallyafter the abrasion step is complete. Secondly, the complexing agent isbelieved to form a complex with the oxidized metal and not theunderlying unoxidized metal thereby limiting the depth of the oxidizedlayer. The complexing agent will be present in the CMP slurry of thisinvention in an amount ranging from about 0.5 to about 5.0 weightpresent and preferably in an amount ranging from about 1.0 to about 3.0weight percent.

Other well known polishing slurry additives may be incorporated into thechemical mechanical polishing slurry of this invention. One class ofoptional additives are inorganic acids and/or salts thereof which may beadded to the polishing slurry to further improve or enhance thepolishing rate of the barrier layers in the wafer, such as titanium andtantalum. Useful inorganic additives include sulfuric acid, phosphoricacid, nitric acid, HF acid, ammonium fluoride, ammonium salts, potassiumsalts, sodium salts or other cationic salts of sulfates, phosphates andfluorides.

BTA, or other film forming agents in the CMP slurry of this inventionmay destabilize the uniform dispersion of abrasive in the slurry. Inorder to promote stabilization of a CMP slurry of this invention againstsettling, flocculation, and decomposition, a variety of optional CMPslurry additives, such as surfactants, stabilizers, or dispersingagents, can be used. If a surfactant is added to the CMP slurry, then itmay be an anionic, cationic, nonionic, or amphoteric surfactant or acombination of two or more surfactants can be employed. Furthermore, ithas been found that the addition of a surfactant may be useful toimprove the within-wafer-non-uniformity (WIWNU) of the wafers, therebyimproving the surface of the wafer and reducing wafer defects.

In general, the amount of additive such as a surfactant that may be usedin the present invention should be sufficient to achieve effectivestabilization of the slurry and will typically vary depending on theparticular surfactant selected and the nature of the surface of themetal oxide abrasive. For example, if not enough of a selectedsurfactant is used, it will have little or no effect on CMP slurrystabilization. On the other hand, too much surfactant in the CMP slurrymay result in undesirable foaming and/or flocculation in the slurry. Asa result, stabilizers such as surfactants should generally be present ina range between about 0.001% and 2% by weight, and preferably from about0.01 to about 1.0 weight percent. Furthermore, the additive may be addeddirectly to the slurry or treated onto the surface of the metal oxideabrasive utilizing known techniques. In either case, the amount ofadditive is adjusted to achieve the desired concentration in thepolishing slurry. Preferred surfactants include dodecyl sulfate sodiumsalt, sodium lauryl sulfate, dodecyl sulfate ammonium salt, and mixturesthereof. Examples of useful surfactants include TRITON® DF-16manufactured by Union Carbide, and SURFYNOL® manufactured by AirProducts and Chemicals.

The CMP slurry of this invention includes an abrasive. The abrasive istypically a metal oxide abrasive. The metal oxide abrasive may beselected from the group including alumina, titania, zirconia, germania,silica, ceria and mixtures thereof. The CMP slurry of this inventionpreferably includes from about 1.0 to about 15.0 weight percent or moreof an abrasive. It is more preferred, however, that the CMP slurry ofthis invention includes from about 3.0 to about 6.0 weight percentabrasive.

The metal oxide abrasive may be produced by any techniques known tothose skilled in the art. Metal oxide abrasives can be produced usingany high temperature process such as solgel, hydrothermal or, plasmaprocess, or by processes for manufacturing fumed or precipitated metaloxides. Preferably, the metal oxide is a fumed or precipitated abrasiveand, more preferably it is a fumed abrasive such as fumed silica orfumed alumina. For example, the production of fumed metal oxides is awell-known process which involves the hydrolysis of suitable feedstockvapor (such as aluminum chloride for an alumina abrasive) in a flame ofhydrogen and oxygen. Molten particles of roughly spherical shapes areformed in the combustion process, the diameters of which are variedthrough process parameters. These molten spheres of alumina or similaroxide, typically referred to as primary particles, fuse with one anotherby undergoing collisions at their contact points to form branched, threedimensional chain-like aggregates. The force necessary to breakaggregates is considerable. During cooling and collecting, theaggregates undergo further collision that may result in some mechanicalentanglement to form agglomerates. Agglomerates are thought to beloosely held together by van der Waals forces and can be reversed, i.e.,de-agglomerated, by proper dispersion in a suitable media.

Precipitated abrasives may be manufactured by conventional techniquessuch as by coagulation of the desired particles from an aqueous mediumunder the influence of high salt concentrations, acids or othercoagulants. The particles are filtered, washed, dried and separated fromresidues of other reaction products by conventional techniques known tothose skilled in the art.

A preferred metal oxide will have a surface area, as calculated from themethod of S. Brunauer, P. H. Emmet, and I. Teller, J. Am. ChemicalSociety, Volume 60, Page 309 (1938) and commonly referred to as BET,ranging from about 5 m² /g to about 430 m² /g and preferably from about30 m² /g to about 170 m² /g. Due to stringent purity requirements in theIC industry the preferred metal oxide should be of a high purity. Highpurity means that the total impurity content, from sources such as rawmaterial impurities and trace processing contaminants, is typically lessthan 1% and preferably less than 0.01% (i.e., 100 ppm).

In this preferred embodiment, the metal oxide abrasive consists of metaloxide aggregates having a size distribution less than about 1.0 micron,a mean aggregate diameter less than about 0.4 micron and a forcesufficient to repel and overcome the van der Waals forces betweenabrasive aggregates themselves. Such metal oxide abrasive has been foundto be effective in minimizing or avoiding scratching, pit marks, divotsand other surface imperfections during polishing. The aggregate sizedistribution in the present invention may be determined utilizing knowntechniques such as transmission electron microscopy (TEM). The meanaggregate diameter refers to the average equivalent spherical diameterwhen using TEM image analysis, i.e., based on the cross-sectional areaof the aggregate. By force is meant that either the surface potential orthe hydration force of the metal oxide particles must be sufficient torepel and overcome the van der Waals attractive forces between theparticles.

In another preferred embodiment, the metal oxide abrasive may consist ofdiscrete, individual metal oxide particles having a primary particlediameter less than 0.4 micron (400 nm) and a surface area ranging fromabout 10 m² /g to about 250 m² /g.

Preferably, the metal oxide abrasive is incorporated into the aqueousmedium of the polishing slurry as a concentrated aqueous dispersion ofmetal oxides, which aqueous dispersion of metal oxide abrasivestypically ranges from about 3% to about 45% solids, and preferablybetween 10% and 20% solids. The aqueous dispersion of metal oxides maybe produced utilizing conventional techniques, such as slowly adding themetal oxide abrasive to an appropriate media, for example, deionizedwater, to form a colloidal dispersion. The dispersion is typicallycompleted by subjecting it to high shear mixing conditions known tothose skilled in the art. The pH of the slurry may be adjusted away fromthe isoelectric point to maximize colloidal stability.

It is desirable to maintain the pH of the CMP slurry of this inventionwithin a range of from about 2.0 to about 12.0, and preferably betweenfrom about 4.0 to about 9.0 in order to facilitate control of the CMPprocess. Slurry handling problems and substrate polishing qualityproblems are encountered when the pH of the CMP slurry of this inventionis too low, e.g., less than 2. The pH of the CMP slurry of thisinvention may be adjusted using any known acid, base, or amine. However,the use of an acid or base that contains no metal ions, such as ammoniumhydroxide and amines, or nitric, phosphoric, sulfuric, or organic acidsare preferred to avoid introducing undesirable metal components into theCMP slurry of this invention.

Although the CMP slurry of this invention may be used to polish any typeof metal layer, the chemical mechanical polishing slurry of thisinvention has been found to have a high copper, titanium, titaniumnitride, and tantalum nitrate and acceptable tantalum polishing rates.In addition, the chemical mechanical polishing slurry exhibits desirablelow polishing rates towards the dielectric insulating layer.

The CMP slurry of this invention may be produced using conventionaltechniques known to those skilled in the art. Typically, the oxidizingagent and other non-abrasive components, are mixed into an aqueousmedium, such as deionized or distilled water, at pre-determinedconcentrations under low shear conditions until such components arecompletely dissolved in the medium. A concentrated dispersion of themetal oxide abrasive, such as fumed alumina, is added to the medium anddiluted to the desired loading level of abrasive in the final CMPslurry.

The CMP slurries of the present invention may be supplied as one packagesystem (oxidizing agent, abrasive, film forming agent and passivatingagent in a stable aqueous medium). To avoid possible CMP slurrydegradation, however, it is preferred that at least a two package systemis used where the first package comprises the film forming agent and anyoptional additives, and the second package comprises the aqueousabrasive dispersion and an oxidizer. The remaining component, thecomplexing agent, may be placed in either the first container, thesecond container or in a third container. Other two-containercombinations of the ingredients of the CMP slurry of this invention arewithin the knowledge of one having ordinary skill in the art.

A multi-package CMP slurry system may be used with any standardpolishing equipment appropriate for use on the desired metal layer ofthe wafer. The multi-package system includes one or more CMP slurrycomponents in, where appropriate, aqueous or dry form in two or morecontainers. The multi-package system is used by combining the componentsfrom the various containers in the desired amounts to give a CMP slurrycomprising at least one oxidizing agent, a film forming agent, acomplexing agent and at least one abrasive in the amounts describedabove.

The CMP slurry of the present invention does not significantly increasethe silicon dioxide polishing rate. However, the CMP slurry of thisinvention polishes copper, titanium, titanium nitride, tantalum, andtantalum nitride layers at good rates under controllable conditions.Thus, the CMP slurry of this invention is effective in controllingpolishing selectivities of titanium, copper, and titanium nitride. Thepolishing slurry of the present invention may be used during the variousstages of semiconductor integrated circuit manufacture to provideeffective polishing at desired polishing rates while minimizing surfaceimperfections and defects.

EXAMPLES

We have discovered that a CMP slurry including at least one oxidizer, acomplexing agent and a film forming agent is capable of polishingmultiple metal layers comprising copper alloys, titanium, and titaniumnitride at high rates while exhibiting an acceptable low polishing ratetowards dielectric layers.

The following examples illustrate preferred embodiments of thisinvention as well as preferred methods for using compositions of thisinvention.

EXAMPLE 1

Electrochemical tests are used to evaluate CMP mechanisms and to provideguidance in selection of slurry components. The electrochemical cellused was developed in the IBM Laboratories and is described in V. Brusicet al., Corrosion And Inhibition Of Thin Line Conductors In VLSIStructures, IBM J R&D, 37, 173 (1993), incorporated herein by reference.The electrochemical cell allows for the evaluation of the electrodepotential and the metal dissolution rate of a substrate, with andwithout surface abrasion. The method uses a PAR model 273 potentiostarwith PAR corrosion software.

FIG. 1 illustrates processes governing the dissolution of copper in thepresence of an oxidizer, i.e., 4 weight % ammonium persulfate witheither glycine (1 & 2) or ammonium oxalate (3 & 4), both present in theamount of one percent by weight at pH 5.1. In both cases the anodicTafel slope is quite low, and the difference between the potentiodynamicpolarization curves with and without abrasion is very small. Theelectrochemical cell results indicate that the Cu surface is not coveredby an oxide film. However, copper dissolution is at least twenty timesslower in the presence of ammonium oxalate. In a comparison to glycine,oxalate is a more effective inhibitor to copper dissolution. There isalso a persistent difference in the corrosion potentials, with thepotential in the ammonium oxalate being consistently lower than thepotential measured in glycine, indicating that a preferentialdissolution process would lead to Cu⁺ ions while with glycine, Cu⁺⁺ ionformation is possible.

At higher pHs, oxalate still adsorbs at the copper surface, but ammoniumoxalate also acts to increase the copper dissolution rate throughformation of Cu(NH₃)_(x) ⁺ and Cu(NH₃)_(x) ⁺⁺ complexes. FIG. 2 showsthe dissolution and passivation of copper in 11% H₂ O₂ (curve 1, aftersurface abrasion), the same oxidizer with 1 weight % glycine (curve 2)and the same oxidizer with 1% ammonium oxalate (curve 3). Corrosionpotential is lowest in the presence of ammonium oxalate. Although inammonium oxalate the copper dissolution is enhanced in a comparison toperoxide alone, reaching about 200 nm/min during abrasion, the surfacerepassivation does occur, leading to the dissolution rate after abrasionof only 5.5 nm/min. The additions of small amounts of BTA assure thatthe passivation should occur promptly, with Cu-BTA providing anadditional factor in copper dissolution control. In contrast, copperdissolution in glycine is the same with and without abrasion, reachingthe uncontrollable values of over 300 nm/min without surfacerepassivation.

EXAMPLE 2

Cu and Ti wafers were polished with a CMP slurry using a Strasbaughpolisher at 3 psi down force, 45 rpm table speed, and 50 rpm spindlespeed. The CMP slurry was formulated to vary the concentration ofhydrogen peroxide, ammonium oxalate, benzotriazole and wetting agent asshown in Table 1A. Cu and Ti removal rates were measured. Several ratesfor prior art slurries including hydrogen peroxide and glycine were alsodetermined and reported in Table 1B. All slurries contained aluminaabrasive, with 5% solids. The wetting agent used was Triton DF16manufactured by Union Carbide Chemicals & Plastics Co., Danbury, Conn.Each of the ammonium oxalate containing slurries identified in Table 1Ahad a pH ranging from 7.2 to 7.8.

                  TABLE 1A    ______________________________________    Polishing rates of Cu and Ti in peroxide slurries    Peroxide           Ammonium            Wetting                                      Cu Rate                                             Ti Rate    (H.sub.2 O.sub.2)           Oxalate    BTA      Agent  nm/min nm/min    ______________________________________    7%     0%         0        50 ppm 21.7   80.6    7%     0.5%       0        50 ppm 278    30.7    11%    0.5%       0        10 ppm 251.7  25.4    11%    1.0%       0        10 ppm 402.9  80.4    9%     1.0%       0.04%    30 ppm 170.7  94.1    7%     1.5%       0.08%    10 ppm 304.7  108.6    ______________________________________

                  TABLE 1B    ______________________________________    Peroxide                   Wetting                                      Cu Rate                                            Ti Rate    (H.sub.2 O.sub.2)              Glycine BTA      Agent  nm/min                                            nm/min    ______________________________________    11%       0.1%    0        0      52.8  101.4     8%       1.1%    0        25 ppm 493.7 75.6    11%       2.1%    0        0      778.3 53.4    ______________________________________

The results of the CMP polishing tests set forth in Tables 1A and 1Bshow that CMP slurries of this invention are capable of achievingpreferred copper and titanium polishing rates and selectivitiesincluding a Cu rate of at least 100 nm/min and a Cu:Ti! selectivity ofat most 4:1.

EXAMPLE 3

The reproducability of Cu removal rates and within wafer non-uniformity(WIWNU) results for a CMP slurry containing 11.0 weight hydrogenperoxide, 1.5% ammonium oxalate, 0.04% BTA, 50 ppm of TRITON® DF-16surfactant manufactured by Union Carbide, and 5% alumina abrasive wasevaluated in this Example. The CMP slurry was applied successively tocopper wafers on a Strasbaugh polisher, using 31158 buffed pad with DF200 insert, a 4 psi down force, a table speed of 50 rpm, and a spindlespeed of 50 rpm.

The experimental results, plotted in FIG. 3 demonstrate that the slurrypolishing performance is quite uniform and does not degrade over time.

What we claim is:
 1. A chemical mechanical polishing slurrycomprising:alumina; at least one oxidizer; a complexing agent selectedfrom the group consisting of compounds consisting of citric acid, lacticacid, tartaric acid, succinic acid, oxalic acid, amino acids, and saltsthereof; and a film forming agent wherein the chemical mechanicalpolishing slurry has a pH of from 7.2 to 9.0.
 2. The chemical mechanicalpolishing slurry of claim 1 wherein the complexing agent is ammoniumoxalate.
 3. The chemical mechanical polishing slurry of claim 2 whereinthe ammonium oxalate is present in an amount ranging from 0.5 to about3.0 weight percent.
 4. The chemical mechanical polishing slurry of claim1 wherein the film forming agent is benzotriazole.
 5. The chemicalmechanical polishing slurry of claim 4 including from about 0.01 toabout 0.1 weight percent benzotriazole.
 6. The chemical mechanicalpolishing slurry of claim 1 wherein the oxidizer is a compound thatforms hydroxyl radicals upon reduction.
 7. The chemical mechanicalpolishing slurry of claim 6 wherein the oxidizing agent is selected fromthe group consisting of hydrogen peroxide, urea hydrogen peroxide andcombinations thereof.
 8. The chemical mechanical polishing slurry ofclaim 7 wherein the hydrogen peroxide is present in an amount rangingfrom about 0.3 to about 12 weight percent.
 9. A chemical mechanicalpolishing slurry comprising:alumina; an oxidizing agent selected fromthe group consisting of hydrogen peroxide, urea hydrogen peroxided, andmixtures thereof; a complexing agent selected from the group consistingof citric acid, lactic acid, tartaric acid, succinic acid, oxalic acids,amino acids, salts thereof, and mixtures thereof; and benzotriazole,wherein the chemical mechanical polishing slurry has a pH of from 7.2 to9.0.
 10. A chemical mechanical polishing slurry comprising:from about1.0 to about 15.0 weight percent of an alumina abrasive having aparticle diameter less than 0.400 micron and a surface area ranging fromabout 10 m² /g to about 250 m² /g; from about 0.3 to about 12.0 weightpercent hydrogen peroxide; from about 1.0 to about 3.0 weight percentammonium oxalate; and from about 0.01 to about 0.2 weight percentbenzotriazole, wherein the chemical mechanical polishing slurry has a pHof from 7.2 to 9.0.
 11. The chemical mechanical polishing slurry ofclaim 9 including at least one surfactant.
 12. The chemical mechanicalpolishing slurry of claim 9 wherein the complexing agent is selectedfrom the group succinic acid, amino acids, lactic acid, salts thereof,and mixtures thereof.
 13. The chemical mechanical polishing slurry ofclaim 9 wherein the complexing agent is ammonium oxalate.
 14. Thechemical mechanical polishing slurry of claim 13 wherein the oxidizingagent is urea hydrogen peroxide.
 15. The chemical mechanical polishingslurry of claim 13 wherein ammonium oxalate is present in the slurry inan amount ranging from about 1.0 to about 3.0 weight percent.
 16. Thechemical mechanical polishing slurry of claim 13 wherein thebenzotriazole is present in the slurry in an amount ranging from about0.01 to about 0.2 weight percent.
 17. The chemical mechanical polishingslurry of claim 13 wherein the oxidizing agent is hydrogen peroxide. 18.The chemical mechanical polishing slurry of claim 13 wherein theabrasive is at least one metal oxide.
 19. The chemical mechanicalpolishing slurry of claim 13 wherein the abrasive is an aqueousdispersion of a metal oxide.
 20. The chemical mechanical polishingslurry of claim 13 wherein the abrasive has a surface area ranging fromabout 5 m² /g to about 430 m² /g.
 21. The chemical mechanical polishingslurry of claim 13 wherein the abrasive is selected from the groupconsisting of precipitated abrasives or fumed abrasives.
 22. Thechemical mechanical polishing slurry of claim 18 wherein the metal oxideabrasive is selected from the group including alumina, ceria, germania,silica, titania, zirconia, and mixtures thereof.
 23. The chemicalmechanical polishing slurry of claim 18 wherein the metal oxide abrasiveconsists of metal oxide aggregates having a size distribution less thanabout 1.0 micron and a mean aggregate diameter less than about 0.4micron.
 24. The chemical mechanical polishing slurry of claim 18 whereinthe metal oxide abrasive consists of discrete, individual metal oxidespheres having a primary particle diameter less than 0.400 micron and asurface area ranging from about 10 m² /g to about 250 m² /g.
 25. Thechemical mechanical polishing slurry of claim 13 wherein the abrasivehas a surface area of from about 30 m² /g to about 170 m² /g.